On the magnetism of grain boundary phase and its contribution to the abnormal openness of recoil loops in hot-deformed magnets

Abstract

The magnetism of grain boundary (GB) phase plays a critical role in the coercivity of Nd–Fe–B magnets. In this work, the aggregation of the GB phase was formed in the hot-deformed magnet due to the low-density high-velocity compaction (HVC) precursor. The ferromagnetism of GB aggregation was confirmed by the analysis of 57Fe Mössbauer spectrometry, and its correlation to the magnetic performance was investigated by micromagnetic simulation. Results show that the soft magnetic GB aggregation is responsible for the low coercivity of the hot-deformed magnet. Moreover, an abnormal large openness of the recoil loop under the reversal magnetic field HR was presented in this work, and the underlying mechanism is interpreted by introducing demagnetization energy. To compensate for the problem of low density, low-melting-point Nd70Cu30 powders were added into the HVC magnet, which makes the GB aggregation paramagnetic and enhances the coercivity.

Macroscopic phenomenon of exchange coupling and microscopic effect on magnetization reversal in sintered Nd–Fe–B magnets

“…The partially enlarged details circled in figure 1 are shown in figures 2(b) and (c), and it can be seen that the openness of recoil loops exists in both samples. The openness of recoil loops originates from the exchange coupling overcoming the anisotropy in the recoil process [26], and the magnetically soft phase can amplify the openness [26,27]. Therefore, in both samples there exists a soft magnetic phase and the exchange couplings are effective even though their strengths are different in these two samples.…”

Tuning Fe2Ti Distribution to Enhance Extrinsic Magnetic Properties of SmFe12-Based Magnets

“…The data obtained using the instruments and testing methods described above are sufficient to support the results of this study. Due to limitations in our conditions, we did not employ the more precise Mössbauer spectroscopy [19,20] to measure the material's purity and magnetic properties.…”

57Fe Mössbauer spectrometry: A powerful technique to analyze the magnetic and phase characteristics in RE–Fe–B permanent magnets*

“…Low-meltingpoint Nd 70 Cu 30 powders were chosen to compensate for the disadvantages of low density. [50] Here, the phase content and magnetism of the different types of GB phases changing with the preparation process in the MQ powder, hot deformation (HD) magnet, and the Nd 70 Cu 30 -added hot deformation magnet (NdCu HD) were investigated by 57 Fe Mössbauer spectrometry. The fitted spectra are depicted in Fig.…”

“…Refined values of the hyperfine parameters for MQ powder, HD magnet, and NdCu HD magnet recorded at different temperatures. [50] Sample T HD magnet measured at 77 K, 300 K, and 473 K. [50] 3.3. A worm-like amorphous phase distributed in 2:14:1 grains…”

“…15. (a) Mössbauer spectra of the MQ powders, HD magnet, and NdCu HD magnet measured at 300 K. (b) Mössbauer spectra of HD magnet measured at 77 K, 300 K, and 473 K [50].…”